Returns true when the conditions (cycles or seconds elapsed) are met. The first
cycle doesn't count (so e.g. "every(100)" will be true at 100, 200,
etc.)

Thanks to Dr.Ruud on comp.lang.perl.misc for helping with this idea, and to
Jerry Hedden for cleaning it up. Thanks to Ben Morrow for getting
Devel::Callsite started, which module is essential to Every.